The goblin-Apult!" -goblin ammo costs 6 turns to research
It does exactly what it says, when fired it "catapults" a goblin spiker cross the battlefield to the designated space. The goblin takes a random amount of damage (if possible) and can then move normally. If the goblin hits a building there is a 10% chance that the building is converted, if it hits a unit theres a 20% chance that the enemy unit dies leaving the goblin in its place. The goblin always dies after hitting a structure. 2 turn cooldown time.

Burning ammo
Costs 4 turns to research
The catapult fires flaming ammo that causes medium burning damage to the target. Does large damage to buildings.

Skull ammo
Costs 6 turns to research
Fire the heads of your enemy back at them! Has a 30% chance to cause fear to every unit with 1 of the shot, leaves a corpse where it hits. Has no effect on undead or ents.

As you can see the first ammo (the only one we have in game) should have had a chance to convert the building and 20% chance to kill any target (good for trying killing strong units). also the goblin wasn't supposed to die when hitting a unit but only when hitting buildings (that might have been converted).

the 2nd type was the most useful for orcs that have no ranged siege and have no way to deal with ships.

the 3d type was a strategic kind of ammo and could have been good to deal with a swarm of ranged units (lowering the attack of many low attack units is useful).

On paper that was a great unit but as it is now is an incredibly worthless piece of unit that sacrifice another unit to deal a mere 8 damage...

Something seriously useless, as you can see.

I suggest to try, at least, the burning ammo and another kind like the skull ammo or at least a kind that deal a low splash damage. For example i might suggest a ammo called "scrap ammo" that should hit AoE in a range of 2 or 3 (around the tile targeted) with a low damage (like 8-10)